1. Field of the Invention
The present invention relates to a method and an apparatus for generating acceleration and deceleration patterns for control of a robot in a servo system which is equipped with a plurality of driving axes so constituted as to mutually exert dynamic interference, in a manner to shorten the required time of movement by such patterns adequate to draw out the maximum power from a driving source.
2. Description of the Prior Art
One of the effective indexes in examining the kinetic capability of a robot is a working tact time. It is preferable that the tact time is minimized and that no unnecessary vibration is concomitant.
Some methods have been proposed heretofore for minimizing the tact time. One of them is carried out by optimizing an acceleration-deceleration curve relative to a servo system.
First, with reference to FIGS. 10 and 11, a brief description will be given on the exemplary method proposed by the present applicant as disclosed in Japanese Patent Application No. Hei 2 (1990)-283867, now Japanese Published Application No. 4-157508.
Denoted by a in FIG. 10 is an acceleration-deceleration curve, where the time required for the velocity .omega. to reach its peak value (.omega.p) from an acceleration start instant (t=0) is termed "peak time" (hereinafter abbreviated to Tp), and in contrast with an acceleration pattern until such peak time, a deceleration pattern is obtained by execution of a temporal reflection with respect to t=Tp.
The acceleration-deceleration curve a is determined by changing the peak time Tp in accordance with the displacement.
More specifically, as shown in FIG. 11, there is previously prescribed the characteristic with respect to the displacement (.DELTA..theta.) and the peak time Tp, and in generating acceleration and deceleration patterns, first an acceleration pattern is generated in such a manner that the time required for the velocity to reach the peak value from the acceleration start point becomes equal to the peak time corresponding to the displacement, and thereafter a deceleration pattern is generated by the technique of temporal symmetrization.
Although the method mentioned above is considered to be sufficiently effective in a servo system in the situation wherein there is no dynamic interference between a plurality of driving axes as in an orthogonal type robot, a problem arises in the case such a method is applied to a multiaxial scalar type robot.
FIG. 12 schematically shows the motion of a biaxial scalar type robot b. In this robot, a second arm b2 is rotatably connected to the fore end of a first arm b1.
FIG. 12A shows the situation wherein the two arms b1, b2 have rotated through an angle .DELTA..theta.1 with the two arms b1 and b2 linearly extended, and FIG. 12B shows the situation after rotation through an angle of .DELTA..theta.1 with the second arm b2 at an angle with respect to the first arm b1. In both cases, the rotation angle .DELTA..theta.2 of the second arm b2 is zero.
As will be understood by careful observation of the motions of both arms, the control aspect becomes different depending on the relationship between the arms b1 and b2. With respect to the moment of inertia at the center of rotation of the first arm b1, the moment in the situation shown in FIG. 12A is greater than that shown in FIG. 12B, so that greater power is needed in the former even though the two motions have the same displacement .DELTA..theta.1. A longer time is also required before the movement comes to a halt.
That is to say, if the acceleration and deceleration patterns for each arm are generated using the same concept as that applied to orthogonal type robots irrespective of the circumstances, it follows that the same peak time Tp is used in both of the situations shown in 12A and 12B.
Therefore, the robot b is actuated with a greater Tp value as compared with the situation shown in FIG. 12B. This lengthens the tact time (2.multidot.Tp).
In an attempt to eliminate such a disadvantage, it is possible to consider changing the peak time Tp in accordance with the displacements .DELTA..theta.1 and .DELTA..theta.2 of the arms.
However, correct determination of such a change requires a lot of experience and is highly dependent on the operator's level of experience and ability. Even if a satisfactory result is attained, there still remains the possibility that the best selectable setting is not achieved or that some additional operations may be needed in case the normal operation fails to completely meet the requirements.
For example, it may be possible to contrive a method of first dividing the operations into a number of probable cases, empirically determining optimal Tp values for each case, subsequently writing the optimal values into ROMs or the like, and using such values as references in generating acceleration and deceleration patterns. However, a lot of complicated work is necessary in order to complete the ROMs, and such must be repeated during the development of every new robot.